This is something that has been playing on my mind lately. My choice would be my parents and I think DH would be ok with this but we have not discussed this. If they couldnt do it for what ever reason I would be stuck choosing between my brother and his wife and a close friend of mine whom the boys see once every week or 2 and adore. She loves the kids and currently has no kids of her own or a partner.
Of course there is also point that DH may want his sister instead.

Its not an easy decision and not an easy discussion to bring up.